Plastic processing machines include various types of machines for forming manufactured articles from plasticly moldable material. These include plastic molding machines of the injection molding type, blow molding machines, extruders, and other such plastics processing apparatus. The VT series injection molding machines manufactured by Cincinnati Milacron of Cincinnati, Ohio are examples of plastic processing machinery of the type to which the present invention relates. Such machines operate in accordance with a processing sequence by which plastic material is usually heated or otherwise plasticized, forced into contact with mold surfaces or other forming devices, set, then ejected as a formed part.
In general, the operation of such molding machines includes the movement of pistons, clamps, screws, conveyors, ejectors and other mechanisms, the control of feeders, valves, cooling elements, pumps, solenoids and other devices, and the communication of process commands and information between the machine and an operator. To facilitate this operation, such machines have been equipped with logic process controllers for programmably controlling the operating sequence of the various machine elements so that the machine operates more efficiently and in accordance with a repeatable and more reliable process. It is known in the art to make such logic controllers programmable by using dedicated programmable controllers programmed in accordance with well known ladder logic techniques, or with any one of a number of alternative programming methods, many of which make use of state of the art microprocessors.
Programmable logic controllers have, in the machines of the prior art, been interfaced with operator stations through which data, setpoints, and other commands may be input by an operator for use by the logic controller program in operating the machine. This has motivated the development of control systems which perform in accordance with digital techniques. It has been found, however, that the operation of such machines in accordance with the processes which utilize digital techniques, and which most effectively use the digital capabilities of the programmable controllers, do not result in the most desirable performance of the machines. Such digital functions work effectively with a control of solenoids, certain valves, switches and other discrete state machine components by which the processes of a machine may in part be implemented, but such digital techniques have not alone provided the capabilities of analog control where optimization analog parameters such as temperatures, pressures, machine part and material velocities, etc., is needed to achieve the desired quality of the process and the product.
Accordingly, control systems have been developed, such as the DPC-270 control system manufactured by Cincinnati Milacron, Inc., Electronic Systems Division, Lebanon, Ohio and described in the manufacturer's publication assembly No. 7-000-05378C, published by Cincinnati Milacron Marketing Company 1987, and expressly incorporated herein by reference. The DPC-270 control system includes an operator station through which data is entered in digital form by an operator and setpoints and prompts are displayed on an operator panel. The information is communicated from the operator station to and from a programmable logic controller having a special purpose dedicated programmable processor and architecture which control the real time process steps and operating sequence of a molding machine. The DPC-270 employs a combination of both digital and analog control signals which it delivers to the machine, and a combination of digital and analog measurement signals which it receives from the machine.
The increased degree of sophistication of such machine controls and of the processes by which they are controlled has increased the need for more effective and efficient communication between the operator and the process being controlled. The reliability and efficiency of the process has been recognized as largely dependent upon the availability of process information to the operator and supervisors of the process and machine and upon the ability of the operator to communicate and control and modify parameters of the programmed controller. This has resulted in the need for effective access and display of clear information regarding machine performance and process parameters as well as the ability to analyze and modify information regarding the process progression and machine status. The requirements of real time machine and process control and those of effective operator interface and process analysis are different. Attempts in the prior art at improvements in the systems have involved compromise of one objective or the other.
Requirements for information transfer between the machine and the operator rapidly change. Changes in the process and operation of the machinery being controlled is less rapid. In addition, the logic process control program is, by its nature, very machine specific and application specific. Most machine specific functions require initial controller configuration but little or no change thereafter. Many application specific functions require occasional reprogramming or setting of the machines, but little or no controller reconfiguration. Effective communication between the operator and the machine so as to provide the most useful process analysis and control requires more frequent programming changes, an operation which, with controllers of the prior art, has been an engineering intensive operation. This is particularly the case where analog control of the machine is employed. In addition, there are real time functions of the machine which must be accessible to immediate operator intervention and control. The systems of the prior art have not efficiently and simultaneously addressed these different requirement needs. Accordingly, there is a need for operator efficiency and capability in the plastics processing machine art.